I am building a computer for my uncle and I came across a problem. I installed everything right and when I went to turn it on it beeped a long one and two short beeps. I have tried different RAM, different hard drive, different power supply but it still did not work. If it is the video card I can not do anything about it. I do not have another video card and my mobo does not have built in video. Help would be appreciated.

And make sure you have a known good working monitor and power cables for both the PC and monitor,
and make sure the monitor is powered on.

and before when even get down to it , Make sure you have a large enough power supply.
Dont even waste your time doing this if you are trying to boot a system with 2 X1950XTXs in crossfire, and 6 Hardrives with a 300 Watt power supply.

Ok Lets Start

1. REMOVE the motherboard, place it on a Plastic surafce/ such as a rubber mat, or a large square of packing material.

2. Start putting the ram, cpu & heatsink/fan, videocard (some videocards Need additional power make sure you are plugging power into these places as well). ONE thing at a time, double check and make sure everything is in place properly and plugged in I.E. CPU fan.

3. Plug the power supply into the board (some boards require additional power, make sure you are plugging the power into these places as well),

4. Take your case and move it by the board and plug the powerswitch onto the CORRECT pins on the motherboard.(consult your motherboards manual if you dont know where these are)

5. Also try hooking up the small speaker in your pc to the CORRECT pins on the mobo to get a diagnostic beep code. (consult your motherboards manual if you dont know where these are)

6. Hook up the monitor to the back of the videocard, carefully, its not screwed down so it can pop out easily. (if your using onboard video this step does not pertain to you)
If you have onboard video just plug it into the VGA port of the back of the motherboard.

7. Press the power button.

Did you hear any Beeps? any video?

If you still dont have video try this only if you have both onboard video and a Slot based videocard I.E. PCI-E/AGP/PCI pull the Slot based video card and try the onboard)

still none?

If you still dont have any video, Try replacing the easiest compents first, such as Ram, then Videocard, then PSU, then CPU, then Motherboard. Just ONE at a time and try booting and listening for beeps after each one.

Make sure you have known good working Componets your replacing them with as well, and make sure they are compatible.